A butt joint used in working with wood materials may include splines or dowels. The splines and the dowels are all hidden when the joint is fully assembled. It is common to use glue between the splines, dowels and wood pieces being interconnected and then clamps are applied to hold them in compression while the glue dries.
This procedure is time consuming and expensive and requires special equipment.
Another problem with the typical hidden joint is that the dowel or the spline is sized precisely to the mortice into which it fits in both of the pieces being connected. If there is the slightest disalignment of the pieces the splines and dowels will not line up making the joint difficult, if not impossible.
A further problem encountered with plank type doors is that the vertical grooving makes it difficult, if not impossible, to give a tight weather seal along the top inside edge of the door due to the grooves remaining open and allowing air and moisture to move from the ouside to the inside. The weatherstripping cannot seal tightly against the grooved surface.